Mpp - Page 323 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st December 2011, 08:28 AM   #3221
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
Default quick question...

Hi Joachim, maybe I am "schief gewickelt" but I have a quick question, as per attached picture of the input stage of the starless phono stage. I am planning to build transimpedance (no problem there), but then I thought to put jumpers and try transconductance as well.

I believe that ground connection (circled red) should not be there - if it were, the lower half of the circuit would not contribute anything, is my thinking correct? I thought I ask before a few hours debugging.....

thanks in advance
Attached Images
File Type: jpg starless question.jpg (134.8 KB, 203 views)
  Reply With Quote
Old 1st December 2011, 09:59 AM   #3222
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
That question came up earlier in this thread. The ground connection looks strange but the circuit works nevertheless. There was also a simulation done by our friend in Litunia and i think he also build it and made it work. Somehow this floating double cascode, symmetric mirror is strange anyway. It did not simply fly out of my head but was a reaction to the question what can be done to fight the P-Channel problem. It was also inspired by the CEN-SEN thread. There i contributed a DC coupled version that also used current mirrors.
So the Starless would not exist without this forum.
  Reply With Quote
Old 1st December 2011, 11:40 AM   #3223
hesener is offline hesener  Germany
diyAudio Member
 
Join Date: Mar 2005
Location: Munich, Germany
OK thanks. Thinking about it, without the ground connection the input JFET would act as a source follower against the (high) drain impedance of the lower cascade, current possibly would not change and so there would be no output signal, I guess. But with the ground connection, the upper half works as an amplifier, and the lower half as a current source into the output node without much contribution. I would expect the transimpedance version to have higher gain, as both halves will contribute (if it actually can be compared.... what is the input voltage at 0 input impedance?)

will try both. Today I should be able to fix it all..... thanks for the help, much appreciated!
  Reply With Quote
Old 1st December 2011, 12:27 PM   #3224
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Yes, thatīs the way i see it too, Gm stage loaded by a constant current source plus RIAA.
Curiously in praxis the transconductance version can sound louder. That is when you use
a cartridge with rather high impedance like the DL103. Itīs 40 Ohms give less gain with the transimpedance version because the 40 Ohm react like degeneration. You get less distortion but also less gain. That was a problem our Litunia contributor had in the beginning. I then added the helper transistors ( raises the output impedance of the mirror times 2 for 6dB more gain ) and we raised the values a bit in the RIAA, so he got around 60dB of gain in the end. The transconductance circuitīs gain is independent of the cartridge impedance because the gate of the Fet isolates the cartridge from the amplification chain.
  Reply With Quote
Old 1st December 2011, 01:32 PM   #3225
sampler is offline sampler  Lithuania
diyAudio Member
 
Join Date: Jan 2010
Hi hesener,
Quote:
Originally Posted by hesener View Post
But with the ground connection, the upper half works as an amplifier, and the lower half as a current source into the output node without much contribution.
Correct, but the lower part actually contributes half the sqrt root of total noise. It could be made quieter.
Quote:
Originally Posted by hesener View Post
I would expect the transimpedance version to have higher gain, as both halves will contribute.
Well no, in both arrangements lower cascode and mirror is acting only as ccs. We discussed gain issues and differences with Joachim quite thoroughly I guess. I built it "as is" only because I could drop in p/n fet input pair for comparison without any major changes, plus servoing "lazy" lower current mirror gives good results so dc coupling is possible but I'm still experimenting on this. Actually for usual transconductance input, circuit can be rearranged to SE. It has lower noise, same open loop bandwith, gain and thd distribution. Coupling cap comes as penalty. I already build 1 channel, and that zener referenced ccs has very good tempco stability. If going for ultimate noise characteristics, 4x2sk170 can be paralleled, but J310 wont cut it for cascoding, PN4391 would do ok.
Attached Images
File Type: png Starless_SE.PNG (28.6 KB, 190 views)
  Reply With Quote
Old 1st December 2011, 01:45 PM   #3226
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
If you run the buffer on +- supply you can place the cap inside, then you can use a much smaller and better one...like the Rel tin polystyrene.
  Reply With Quote
Old 1st December 2011, 02:01 PM   #3227
sampler is offline sampler  Lithuania
diyAudio Member
 
Join Date: Jan 2010
Quote:
Originally Posted by MiiB View Post
If you run the buffer on +- supply you can place the cap inside, then you can use a much smaller and better one...like the Rel tin polystyrene.
Yes MiiB, all the usual tricks are valid if using bipolar supply. Even zener ccs could be servoed for dc coupling. I'm still working on this, it's just lack of spare time that is slowing me down these days.
  Reply With Quote
Old 1st December 2011, 02:09 PM   #3228
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Sampler, mighty fine SE circuit you made !
There is only the bleeder resistor missing over Q9.
Several J310 can be paralleled for more juice.
  Reply With Quote
Old 1st December 2011, 02:26 PM   #3229
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
On thing I like with the single ended...is the way the current is set through the input via the current source in the second leg...with this circuit the BF862 would be at very very good part, since they can operate at lover currents and still be quiet, but at the expense of DC coupling...
  Reply With Quote
Old 1st December 2011, 02:33 PM   #3230
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I think the Starless idea develops into something very interesting.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 12:35 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2